This patent specification is in the field of methods and equipment for assisting medical professionals in assessing a patient's cardiovascular and vertebral/hip fracture risk and bone condition parameters such as bone mineral density (BMD) using x-ray measurements derived from localization or scout scans taken with a computed tomography (CT) or a quantitative computed tomography (QCT) device and/or scans taken with a dual energy x-ray absorptiometry (DXA) device. In addition, this application pertains to assessing patient risks by using x-ray measurements of other anatomy.
QCT has long been used to estimate BMD. Typically, the patient is positioned on the patient bed of a CT scanner together with a QCT phantom that is in the field of view and has known characteristics. A lateral CT localization or scout scan is taken to identify vertebrae and perhaps to adjust CT gantry angle tilt to place one or more axial CT slices through the center or another selected plane of one or more selected vertebrae. The CT slice images that include the phantom and vertebral bodies such as L1 and L2, or T1 through L3, are processed to derive an estimate of the patient's BMD. This and other approaches to measuring bone mass are discussed in a 1989 paper by Christopher E. Cann.28 (The superscript numerals refer to the documents cited at the end of the detailed description; all of those documents, as well as the patents and patent applications cited in this patent specification, are hereby incorporated by reference herein.) QCT products are commercially offered in this country by a number of companies, including Mindways Software, Inc. of Baltimore, Md. and Image Analysis, Inc. of Columbia, Ky.29,30 See, also, U.S. Pat. No. 4,233,507 and FDA 510(k) document K031991 dated Jul. 30, 2003 regarding a product of Image Analysis, Inc. named DXAVIE Hip and Spine.31 While the lateral localization or scout scan typically taken for a QCT procedure may allow visualization of vertebral fractures and of aortic calcifications, as mentioned in material published by Image Analysis, Inc.30, it is believed that there is no teaching or suggestion of using such CT or QCT lateral scans to quantify vertebral fracture assessment or aortic calcification in an automated manner.
A different modality, dual x-ray energy bone densitometry (DXA), has long been used mainly to obtain bone condition assessment information, including the projected bone mineral density (BMD, in g/cm2) at various anatomical sites. One example of DXA systems is available from Hologic, Inc. of Bedford Mass. under the trade name Discovery. It has an examination table and a C-Arm at opposite ends of which are mounted an x-ray tube and a multi-detector array. The patient is positioned on the examination table between the x-ray tube and the detector array of the C-arm. For the assessment of bone mineral density, the x-ray detector and a fan-shaped beam of x-rays from the tube are scanned as a unit axially along the patient, while the x-rays are alternatively switched between high and low energy ranges. By comparing the relative attenuation of the x-rays at the two energies, the contributions to attenuation due to the soft tissue can be subtracted. In other equipment, dual energy x-ray measurements are obtained by using a steady x-ray beam of relatively broad energy range impinging on detectors that measure respective energy ranges of the beam, or on a detector that can discriminate between energy ranges, such that high and low energy separation is done by the detector. At least in principle, similar results may be obtained without scanning, using an x-ray beam of a sufficient cross-section and a 2D array of detector elements. In each case, an image can be obtained of the bony structure of the body by the soft-tissue subtraction method. This image is then input into BMD analysis, which calculates and reports the BMD. The image can be displayed by showing it on a screen and/or printing it and can be stores in PACS or other storage/retrieval systems together with other densitometry and patient data.
When the patient's spine is scanned with a DXA device, the displayed image is similar to that in conventional spine radiography except that it requires less x-ray exposure and the entire spine or any desired part thereof can be scanned in one pass and shown as a single image. The image also is similar to a localization or scout scan image taken with a CT or QCT device. In DXA, the image can be derived from measurements at both x-ray energy ranges or at one of them (single energy image). In the case of systems such as the Discovery, a single energy image can be obtained by selecting a fixed, relatively narrow energy range rather than alternating between two energy ranges. If a dual energy image is already available but a single energy image is desirable for further processing or another purpose, it can be extracted simply by using only the x-ray detector outputs for one of the energies or by adding the two energies together rather than subtracting them. In systems that use the detector to separate high and low x-ray energy, a single energy image can be extracted by using only the output of only one of the detector sets or at one of the narrower energy ranges, or by adding the high and low x-ray energies together rather than subtracting them.
The options for densitometers offered by Hologic, Inc. include CADfx, which carries out computer processing of the spinal image to help detect vertebral fractures in DXA images, and Instant Vertebral Assessment (IVA), sometimes referred to as vertebral fracture assessment (VFA), wherein vertebral deformities can be evaluated similar to standard radiograph or CT image reading methods. IVA images are lateral spine images typically taken at single energy. While the images produced using DXA IVA are not of sufficient quality for general radiological use, it has been observed that the quality of IVA images is similar to that of abdominal radiographs for visualizing abdominal aorta calcifications (AAC). In fact, AAC can be seen in DXA images sufficiently well to have allowed the Food and Drug Administration (FDA) to clear Hologic, Inc. (510K clearance K060111 approval Apr. 24, 2006) for visualizing AAC with its DXA equipment.
The abdominal aorta is a large, fluid filled vessel comprised of soft tissue. It can be barely visible on conventional x-ray images and is typically is visualized with the use of a radio-opaque contrast material. A vessel that is calcified usually presents with a linear or eggshell calcified pattern which is typical of calcification in the wall of a fluid filled structure. The history of using radiographs to identify abdominal aortic calcifications is well-established.1,2,5,11,14,15,16 A recent (2005) review article of methods for detection of abdominal aortic calcifications describes three primary methods: plain radiograph, ECT, and CT. It concludes, “Presently no modality has been accepted as the gold standard for the measurement of abdominal aortic calcification,”5 but observes that “The simplest method of detecting abdominal aortic calcification is with plain abdominal X-ray.”5 
Abdominal Aortic Calcification (AAC) is seen anterior to the lumbar spine in lateral view and is graded in severity by several methods8-10 related to the length of the AAC seen in the image. The published literature indicates a graded association between the length of the AAC seen in the image and the risk of future morbidity and mortality.1, 3, 6, 7 In a typical grading scheme, the posterior and anterior walls of the aorta are graded in the area in front of the L1-L4 vertebra for total length of calcifications seen. For example, 0, ≦1 cm, 1 to 2.4 cm, 2.5 to 4.9 cm, ≧5 cm is considered, absent, dubious, mild, moderate, and severe, respectively.10 It has been reported that AAC is diagnostic for arteriosclerosis1-4. AAC is believed to be strongly associated with a number of diseases, independent of traditional clinical risk factors such as age, cigarette use, diabetes mellitus, systolic blood pressure, left ventricular hypertrophy, body mass index, cholesterol, and HDL cholesterol.1, 3, 5-7 The known literature identifies plain radiography, CT and ECT as the modalities to be used for AAC detection and quantification. Published patent application US 2003/0176780 A1 discusses detection and quantification of aortic calcium, but from CT slice images rather than lateral localization of scout images. MRI is also referenced as a modality in connection with assessing atherosclerosis.23 